The vertical COMFET is commonly used for power applications. As is well known in the industry, the COMFET derives its ability to carry relatively large currents by a greatly increased injection of minority carriers from the substrate. The structure, doping levels, and operation of this type of device are described in U.S. Pat. No. 4,364,073, which issued Dec. 14, 1982, to Becke et al.
There are applications for a device that would control current flow in both directions with low forward voltage drop and high current density. By way of example, such potential applications include motor controls for automobile starters, small appliances, and small power tools. A complementary-symmetry COMFET pair could satisfy this requirement. Such COMFET pairs utilizing vertical geometry would require two separate devices, since no simple method for integrating vertical geometry P-channel and N-channel devices on the source chip appears possible. Lateral, N-channel insulated gate transistors (LIGT) are well known and have been disclosed in the literature. See, for example, Simpson et al., "Analysis of the Lateral Insulated Gate Transistor," IEDM Tech. Dig., 1985, pp. 740-743; and Robinson et al., "Lateral Insulated Gate Transistors with Improved Latching Characteristics," IEDM Tech. Dig., 1985, pp. 744-747.
The present invention utilizes this LIGT geometry for structuring a complementry-symmetry COMFET pair on the same substrate.